In some image processing devices applied to television sets and the like, image data (including data in which a predetermined calculation, such as addition and subtraction, is performed to the image data, the same holds true for the following description) processed in past times is used in processing the image data of a processed target. For example, in such image processing devices, it is necessary to sequentially store the processed image data using a frame memory.
On the other hand, recently an amount of image data that should be processed by the image processing device increases continuously with the rapid progress of high definition and high-speed processing of the image data. Therefore, a storage capacity or a transfer capability necessary for the frame memory also increases continuously, and fabrication of the frame memory that meets the needs becomes harder.
For example, Patent Document 1 proposes a coding device in which the amount of data stored in the frame memory is reduced by performing fixed length coding (a coding method in which a coding length (the number of bits) of coded data is uniform).
However, nowadays there is a demand to further reduce the data amount from the viewpoint of simplification and cost reduction of the frame memory. For example, Patent Documents 2 to 5 propose a coding device in which variable length coding (a coding method in which the code length of the coded data may be different) is adopted, and the data amount may be reduced compared with the fixed length coding.